This invention relates to a water-insoluble crosslinked-starch-xanthate composition useful for removing heavy metal ions from aqueous solutions.
In a previous abandoned patent application, Ser. No. 342,134, filed Mar. 16, 1973, herein incorporated by reference, a method was disclosed for removing heavy metal ions from aqueous solutions by precipitating a water-insoluble complex formed from water-soluble cationic polymer, a water-soluble starch-xanthate, and the heavy metal ions. It was also disclosed in the above-mentioned patent application that water-soluble starch-xanthate alone would coprecipitate with the heavy metal ions, but this coprecipitation resulted in a very inefficient heavy metal ion removal which did not meet present-day discharge limits. Because of our previous experience with the use of starch-xanthate in the removal of heavy metal ions from aqueous solutions, we were surprised to discover that heavy metal ions could be effectively removed from aqueous solutions by compositions comprising crosslinked-starch-xanthate having a degree of crosslinking (DCL) such that the crosslinked-starch-xanthate exhibits a degree of swelling in water at 95.degree. C. of from 65% to 450%.
The compositions of this invention have all the objects and advantages disclosed in patent application Ser. No. 342,134, supra.
Crosslinked-starch-xanthate is defined herein as starch which has been crosslinked with the various known crosslinking agents and which is subsequently xanthated. Unless otherwise specified herein, the xanthate will be sodium xanthate.